Question about HSTS max-age

@RobBNL I would asume it is a safe value for the start. When you use it the HSTS instruction is being stored outside your server in a central DB from where the browsers are taking the information. If you do have some misconfiguration, or issue with SSL certificate, it may render your site inaccessible for a long time. So it is better to start with a quick turnaround and when you are sure all is working properly, then you can set a longer period.
Miminum max-age to be included in the preload database is 31536000 seconds (1 year).
More info here: https://hstspreload.org/.